This invention relates to an automatic film developer, and more particularly relates to an automatic film developer which prevents uneven finish during development.
In an automatic film developer, a film which has been exposed is successively passed through a developing tank, a fixing tank, a washing tank, and a drying tank, by a conveyor. In order to provide uniform development, the developing time, temperature, and concentration should always be maintained within certain ranges.
However, in such an automatic film developer, uneven developing finish is sometimes liable to occur, especially with certain kinds of films and developing agents. One of the causes of this is the partial changing of the nature of the fluid in the developing tank. This partial changing is especially apt to occur near the surface of the developing liquid.
This is because of two reasons. One is that oxidation of the developing liquid by air occurs at its surface. The other is because when the developed film is being taken out of the developing tank the developing liquid attached to the film is squeezed off it, and this liquid is thereby exposed to air, and also, because it has been in contact with the film for a long time, it contains a high concentration of free bromine radicals which are isolated from the halogenated silver layer of the film by the reducing agent. Thus the surface of the developing liquid in the tank is liable to be rather different in composition from the fresh developer in the rest of the tank. This is particularly noticeable at the point where the film leaves the tank, where, as explained above, contamination is at its worst. Mixing of this contaminated surface layer cannot be done immediately with the rest of the developer in the tank. Thereby uneven finish in the film's development can occur.
The effect of the contamination of the surface layer is particularly strong at the point where the film enters the tank. Here it is dry, and the very first developer with which it comes into contact, to which it is highly susceptible, owing to its dryness, is this contaminated and non-fresh developer. By this so-called "wetting shock", particularly, uneven finish is caused.
A countermeasure against this which has been practiced is to mix the developer strongly. But, in practice, it has proved almost impossible to mix the developer strongly enough and fast enough, in the restricted space available inside a developing tank, to completely obviate the streaking and uneven finish problem.